1. Field of the invention
The present invention relates to a display apparatus of the cathode ray tube type for displaying using a magnetic field and, more particularly, to a display apparatus which can display information at a reference position on the display screen of the cathode ray tube (hereinafter, abbreviated as the CRT).
The invention also relates to an apparatus for displaying using a magnetic field in which the setting position can be changed.
2. Related Background Art
Such a display apparatus is used in character processing apparatuses such as, for example, a word processor and the like, personal computers, and various kinds of measuring apparatuses. In this type of display apparatus, in general, an electron beam is deflected by a deflection magnetic field, thereby allowing characters, images, and the like to be displayed on the display screen of the CRT. In such a display apparatus, the deflecting coil for generating the deflecting magnetic field is positioned and attached in the throat portion of the CRT in a manner such that the display information is accurately displayed at a reference position, for example, at the center on the display screen of the CRT in consideration of the influence of the electron beam by the Earth's magnetic field.
Therefore, the above display apparatus can properly display a display pattern 13 at a reference position on a CRT 1 in the state in which the length in the lateral direction of the image plane is long as shown in, for example, FIG. 3A.
However, if a display pattern is displayed in the state in which the length in the vertical direction of the image plane is long as shown in FIG. 3B by the apparatus designed so as to display a display pattern in the state in which the length in the lateral direction of the image plane is long as shown in FIG. 3A in consideration of the influence by the Earth's magnetic field there is the following drawback. Namely, the deflecting magnetic field from the deflecting coil improperly acts on the electron beam, so that the display pattern 13 is displayed at a position deviated from the reference position on the screen of the CRT 1 and it is hard to see the display information. Further, in recent years, there is the tendency such that a number of graphic displays are used; therefore, such a drawback is more and more typical in the current situation in which it is required to freely change the vertical and lateral lengths of the image plane on the CRT.